In optical systems it is sometimes necessary to provide extremely fine spatial or angular alignment of a laser beam. The terminology extremely fine as used here implies spatial alignment changes on the order of a few micrometers (μm) and angular alignment changes of a milliradian (mrad) or less. One example wherein fine alignment is required is steering a laser beam into a single mode core of an optical fiber.
Fine beam alignment (beam steering) is typically done by reflecting a beam from one or more mirrors tilted in one or two axes by some kind of precision actuator. Such actuators include peristaltic actuators, piezoelectric actuators, magnetic actuators and even very fine differential screw mechanisms. In each case, a mechanical linkage is needed between the actuator and the mirror being actuated. Because of this it is possible for a mirror, once aligned to become misaligned, for example, through vibration or shock thereby requiring the mirror to be re-aligned. It would be advantageous to have a more positive fine alignment than current arrangements provide.